Another favorite of mine is the ASHRAE Pocket Handbook. This little gem really will fit in
your back pocket and can be a valuable reference for countless useful pieces of information, like duct or piping friction rates, properties of materials, and in the context of our
current discussion, load check figures, as illustrated below.

In fact the handbook contains the information needed to take your load estimate one step further by including all of the basic information you need to do a manual load calculations using the Cooling Load Temperature Differential (CLTD) method including an outline of the steps in the procedure, the necessary equations, and where the required information can be found in the guide, as illustrated below.

New copies of the handbook can be obtained for under $40 if you are an ASHRAE
member. I have seen used copies for under $15 in used book stores and
on-line, especially the earlier (pre-2005) editions. Given that the rules behind physics
haven’t changed much lately, an older version will probably do just fine.

An important caution regarding using rules of thumb and techniques like the CLTD method; in contrast with modern load calculation programs used by experienced practitioners, they are at best approximations and should generally not be used as the basis for selecting equipment. But, as a technique to get a feel for what you think might be going on in your system or make a first pass assessment of what the load might be as you begin a design or acquisition process, they can serve you well, as they have in my career.
David Sellers
Senior Engineer – Facility Dynamics Engineering